Embodiments of the present specification relate to voltage sensing devices, and more particularly to calibration methods for the voltage sensing devices.
Recently, deregulation of the electricity supply market has led to increased competition between electricity providers. It is now relatively common for companies and households to have a choice of several different electricity providers when deciding on an electricity provider to supply their electricity needs. This has led to competition between the different providers over matters including pricing and quality of supply. Further, sometimes electricity providers need to supply their customers with less expensive electricity while still assuring the same or improved quality of supply to their customers. In order to achieve these goals the electricity providers have to improve the efficiency of electricity networks or electricity distribution system. Furthermore, due to deregulation, network losses and interruption to electricity supply are now being penalized.
Typically, it has been found that even in highly developed countries, approximately 10% of all electricity generated is lost within the electricity networks themselves. For example, a portion of the electricity being transmitted through a current carrying cable, also referred to as a “power line” of an electricity network may be lost as a result of transmission losses. This figure representing electricity loss within the electricity network rises to almost 25% in less developed nations. This loss of power in the electricity network may be due to undetected faults. Further, these faults may go undetected for long periods of time. Moreover, even when the faults are detected, it is usually challenging to locate the faults over an expansive electricity network. By providing the information of the electrical properties in the electricity network (e.g., by monitoring the electricity networks) in an accurate manner, electricity providers may be able to significantly reduce the amount of electricity lost in the electricity networks and make considerable savings in the cost of generating the electricity. Furthermore, by closely monitoring the electricity networks electricity providers will be in a better position to correct faults in the electricity networks swiftly with a minimum of inconvenience to their customers, thereby providing an improved quality of supply to their customers.
A variety of sensors have been developed for measuring a current in a current carrying cable, such as a current carrying cable in a high voltage electricity distribution system. For example, optical current sensors are used to measure the current in the current carrying cable. The optical current sensors are generally based on the Faraday effect. Some optical current sensors use bulk glass or fiber optic cables that surround the current carrying cable. Although the optical current sensors have a very high dynamic range, however, the optical current sensors require opening the current carrying cable at installation, which may be an expensive procedure.
Other kinds of sensors that are used for measuring voltages in the electricity networks may employ metal shells disposed around the current carrying cables. These sensors use the metal shells as capacitance dividers between the current carrying cables and a ground underneath. Among other factors, the capacitance between the shells and the current carrying cables depends on the distance between the shells and the current carrying cables. Accordingly, the metal shells may have limited capacitance between the current carrying cables and the shells themselves because of a limit on a gap between the shells and the current carrying cables. Further, due to the limited capacitance, the sensor may be influenced by changes in surrounding conductors, such as measuring circuits. Moreover, an increase in an area of the shell to increase a capacitance between the shells and the current carrying cables typically results in an increase in a parasitic capacitance of the sensor. The increased parasitic capacitance makes the sensor relatively more prone to fluctuations in the surrounding conductors.
Further, in cases of sensors configured to measure voltage values in the power line, the voltage measurement entails physically connecting the voltage measuring device to the voltage line and to the ground. This physical connection between the voltage measuring device and the ground is required to prevent monitored values being undesirably affected by the presence of any object that may exist between the ground and the voltage measuring device. By way of example, a passing vehicle, a tree, an animal, or a bird, or any other object intentionally or unintentionally disposed in close vicinity of the ground and/or the voltage measuring device may result in undesirable changes in the measurement values of the voltage measurement device in absence of the physical connection between the voltage measuring device and the ground. It may be noted that providing this physical connection between the voltage measuring devices and the ground requires complex installation procedures. For example, such installation procedures are both time consuming and labor intensive resulting in an increase in the cost of installing the voltage measuring device. Further, the physical connection to the ground may need to be maintained and periodically checked.